Method of cooling a spherical object

ABSTRACT

A METHOD OF UNIFORMLY COOLING A SPHERICAL OBJECT, SUCH AS A CAST METAL BALL, BY ROLLING IT ALONG A PAIR OF SPACED TRACKS HAVING DIRRERENT HEIGHTS, SO THAT THE AXIS OF ROTATION CONSTANTLY CHANGES AND HEAT IS EXTRACTED UNIFORMLY FROM THE OUTER SURFACE.

Jan. 1, 1974 w. c TROY 3,783,042

METHOD OF COOLING A SPHERICAL OBJECT Filed July 31, 1972 United States Patent 3,783,042 METHOD OF COOLING A SPHERICAL OBJECT Walter Charles Troy, National City, Calif., assignor to Amsted Industries Incorporated, Chicago, Ill. Filed July 31, 1972, Ser. No. 276,885 Int. Cl. C2141 9/36 U.S. Cl. 148-153 4 Claims ABSTRACT OF THE DISCLOSURE A method of uniformly cooling a spherical object, such as a cast metal ball, by rolling it along a pair of spaced tracks having different heights, so that the axis of rotation constantly changes and heat is extracted uniformly from the outer surface.

This invention relates to a method of uniformly cooling a heated spherical metal object. Certain spherical metal objects, such as steel or cast iron alloy balls utilized in mills, to pulverize material such as coal for firing large boilers, preferably have an uninterrupted outer surface and substantially the same granular structure throughout. In order to obtain maximum performance in such pulverizing operations, the metal objects preferably are hardened by heat treating.

Merely by way of example, ferrous balls of suitable composition might be hardened by heating them to the range of about 1500 to 2000" F., holding them at that temperature for a suitable time, followed by air cooling to room temperature. Obviously, other heat treatments will be used for different alloys.

The present disclosure, however, does not relate to any particular heat treatment but to a method of cooling heated spherical objects uniformly, through any particular temperature ranges, such that the cooling gradient isotherms from the entire outer surface inwardly to the core are spherical in contour and concentric with the ball.

In the drawings:

FIG. 1 is an isometric view of one embodiment of a cooling trough utilized in carrying out the method of this invention; and

FIG. 2 is an end elevational view of the trough with a spherical object resting on the rails formed thereby.

Achieving completely uniform cooling of a spherical body can be difficult, but is essential for uniform hardness and uniform stress patterns in the product. It will be appreciated that in the heat treating of ferrous balls, internal stresses are generated by the events which occur in the hardening of a steel to a suitable hardness for its intended purpose; that is, thermal gradients which are present during the cooling of the object from a high temperature and result in stress due to unequal contrac tion below the plastic flow temperature, and volume changes associated with martensite formation below the M, temperature. To equalize such stresses and avoid any harmful effect therefrom, the spherical object, or ball, is heated to a temperature above the critical transformation range of the particular alloy involved and then cooled uniformly to room temperature to produce cooling gradient isotherms which are spherical in contour and concentric with the ball. This requirement precludes any static position for the ball during the cooling process because in such a position, heat radiation from the upper portion of the object is greater than the heat radiation from the lower portion because of reflected heat from the 3,783,042 Patented Jan. 1, 1974 ice surface supporting the ball. Furthermore, to obtain uniform cooling, the ball must be rotated on a constantly changing axis so that all portions of the outer surface of the ball are exposed for equal lengths of time to the air and to the ball support means.

It has been found, according to the present invention, that such cooling is best accomplished by rolling the heated ball along a pair of parallel tracks having different heights so that the ball rolls on circular paths of different diameters.

In one embodiment of the parallel tracks, a U-shaped trough 10 has spaced, parallel legs 14 and 16 of unequal length, thereby providing running surfaces or tracks 18 and 20 of unequal height. Preferably, because of space limitations and the time required for cooling, the trough may be centrally pivoted in the well-known see-saw arrangement and alternately tilted in opposite directions, or one end of the trough may be hinged while the other end is alternately raised and lowered. In either of these arrangements, the ball 22 rolls back and forth for a length of time suflicient for the ball to cool to the desired tem-- perature. The ball, in each direction of movement, should rotate at least but rotation through 360 or more in each direction is preferred. The spaced tracks impart to the ball a slight rotation about an axis parallel to the tracks which, when combined with the normal rotation of the ball, constantly changes the circles of contact, illustrated as dot-dash lines 24 and 26 in FIG. 2, between the ball and the tracks and causes the ball to rotate on constantly changing axes of rotation. This arrangement serves to extract heat uniformly from the outer surface of the ball thus achieving the optimum cooling gradients mentioned above.

What is claimed is:

1. A method of uniformly cooling a heated spherical object comprising the steps of: supporting the object on a pair of spaced, parallel tracks having different heights, and rolling the object on said tracks until the ball has cooled to the desired temperature.

2. A method according to claim 1 wnerein the tracks are alternately tilted in opposite directions to impart a back and forth rolling motion to the spherical object, and the object is rolled through at least 180' of revolution alternately in each direction.

3. A method according to claim 1 including the steps of pivotally mounting the tracks on a horizontal axis, alternately raising and lowering at least one end of the tracks so that the object is rolled alternately back and forth on the tracks on constantly changing axes of rotation.

4. A method of heat treating a spherical metal object comprising the steps of: heating the object to a temperature above its critical transformation range, supporting the object on spaced tracks the vertical projections of which intersect the object on circular segments having different diameters, and rolling the object on the tracks until it has cooled to the desired temperature.

References Cited UNITED STATES PATENTS 3,201,289 8/1965 Stewart 148153 RICHARD O. DEAN, Primary Examiner U.S. Cl. X.R. 62-62 148-155 

